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aria-current="page" class="active sidebar-link">16_变量进阶(理解)</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/e98ba6/#目标" class="sidebar-link">目标</a></li><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/e98ba6/#_01-变量的引用" class="sidebar-link">01. 变量的引用</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/e98ba6/#_1-1-引用的概念" class="sidebar-link">1.1 引用的概念</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/e98ba6/#_1-2-变量引用-的示例" class="sidebar-link">1.2 变量引用 的示例</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/e98ba6/#_1-3-函数的参数和返回值的传递" class="sidebar-link">1.3 函数的参数和返回值的传递</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/e98ba6/#_02-可变和不可变类型" class="sidebar-link">02. 可变和不可变类型</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/e98ba6/#哈希-hash" class="sidebar-link">哈希 (hash)</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/vdoing-demo-repository/pages/e98ba6/#_03-局部变量和全局变量" class="sidebar-link">03. 局部变量和全局变量</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/e98ba6/#_3-1-局部变量" class="sidebar-link">3.1 局部变量</a></li><li class="sidebar-sub-header level3"><a href="/vdoing-demo-repository/pages/e98ba6/#_3-2-全局变量" class="sidebar-link">3.2 全局变量</a></li></ul></li></ul></li><li><a href="/vdoing-demo-repository/pages/f99095/" class="sidebar-link">17_函数进阶</a></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06225672><div class="articleInfo" data-v-06225672><ul class="breadcrumbs" data-v-06225672><li data-v-06225672><a href="/vdoing-demo-repository/" title="首页" class="iconfont icon-home router-link-active" data-v-06225672></a></li> <li data-v-06225672><a href="/vdoing-demo-repository/python/#Python" data-v-06225672>Python</a></li></ul> <div class="info" data-v-06225672><!----> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2023-04-02</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="">16_变量进阶(理解)<!----></h1> <!----> <div class="theme-vdoing-content content__default"><h1 id="变量进阶-理解"><a href="#变量进阶-理解" class="header-anchor">#</a> 变量进阶（理解）</h1> <h2 id="目标"><a href="#目标" class="header-anchor">#</a> 目标</h2> <ul><li>变量的引用</li> <li>可变和不可变类型</li> <li>局部变量和全局变量</li></ul> <h2 id="_01-变量的引用"><a href="#_01-变量的引用" class="header-anchor">#</a> 01. 变量的引用</h2> <blockquote><ul><li>变量 和 数据 都是保存在 <strong>内存</strong> 中的</li> <li>在 <code>Python</code> 中 <strong>函数 的 参数传递</strong> 以及 <strong>返回值</strong> 都是靠 <strong>引用</strong> 传递的</li></ul></blockquote> <h3 id="_1-1-引用的概念"><a href="#_1-1-引用的概念" class="header-anchor">#</a> 1.1 引用的概念</h3> <p>在 <code>Python</code> 中</p> <ul><li><strong>变量</strong> 和 <strong>数据</strong> 是分开存储的</li> <li><strong>数据</strong> 保存在内存中的一个位置</li> <li><strong>变量</strong> 中保存着数据在内存中的地址</li> <li><strong>变量</strong> 中 <strong>记录数据的地址</strong>，就叫做 <strong>引用</strong></li> <li>使用 <code>id()</code> 函数可以查看变量中保存数据所在的 <strong>内存地址</strong></li></ul> <blockquote><p>注意：如果变量已经被定义，当给一个变量赋值的时候，本质上是 <strong>修改了数据的引用</strong></p> <ul><li>变量 <strong>不再</strong> 对之前的数据引用</li> <li>变量 <strong>改为</strong> 对新赋值的数据引用</li></ul></blockquote> <h3 id="_1-2-变量引用-的示例"><a href="#_1-2-变量引用-的示例" class="header-anchor">#</a> 1.2 <code>变量引用</code> 的示例</h3> <p>在 <code>Python</code> 中，变量的名字类似于 <strong>便签纸</strong> 贴在 <strong>数据</strong> 上</p> <ul><li>定义一个整数变量 <code>a</code>，并且赋值为 <code>1</code></li></ul> <table><thead><tr><th style="text-align:center;">代码</th> <th style="text-align:center;">图示</th></tr></thead> <tbody><tr><td style="text-align:center;">a = 1</td> <td style="text-align:center;"><img src="media/14982751015713/004_a1tag.png" alt="004_a1tag"></td></tr></tbody></table> <ul><li>将变量 <code>a</code> 赋值为 <code>2</code></li></ul> <table><thead><tr><th style="text-align:center;">代码</th> <th style="text-align:center;">图示</th></tr></thead> <tbody><tr><td style="text-align:center;">a = 2</td> <td style="text-align:center;"><img src="media/14982751015713/005_a2tag.png" alt="005_a2tag"><img src="media/14982751015713/005_1.png" alt="005_1"></td></tr></tbody></table> <ul><li>定义一个整数变量 <code>b</code>，并且将变量 <code>a</code> 的值赋值给 <code>b</code></li></ul> <table><thead><tr><th style="text-align:center;">代码</th> <th style="text-align:center;">图示</th></tr></thead> <tbody><tr><td style="text-align:center;">b = a</td> <td style="text-align:center;"><img src="media/14982751015713/006_ab2tag.png" alt="006_ab2tag"></td></tr></tbody></table> <blockquote><p>变量 <code>b</code> 是第 2 个贴在数字 <code>2</code> 上的标签</p></blockquote> <h3 id="_1-3-函数的参数和返回值的传递"><a href="#_1-3-函数的参数和返回值的传递" class="header-anchor">#</a> 1.3 函数的参数和返回值的传递</h3> <p>在 <code>Python</code> 中，函数的 <strong>实参</strong>/<strong>返回值</strong> 都是是靠 <strong>引用</strong> 来传递来的</p> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">def</span> <span class="token function">test</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;-&quot;</span> <span class="token operator">*</span> <span class="token number">50</span><span class="token punctuation">)</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;%d 在函数内的内存地址是 %x&quot;</span> <span class="token operator">%</span> <span class="token punctuation">(</span>num<span class="token punctuation">,</span> <span class="token builtin">id</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span>

    result <span class="token operator">=</span> <span class="token number">100</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;返回值 %d 在内存中的地址是 %x&quot;</span> <span class="token operator">%</span> <span class="token punctuation">(</span>result<span class="token punctuation">,</span> <span class="token builtin">id</span><span class="token punctuation">(</span>result<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">)</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;-&quot;</span> <span class="token operator">*</span> <span class="token number">50</span><span class="token punctuation">)</span>

    <span class="token keyword">return</span>  result

a <span class="token operator">=</span> <span class="token number">10</span>
<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;调用函数前 内存地址是 %x&quot;</span> <span class="token operator">%</span> <span class="token builtin">id</span><span class="token punctuation">(</span>a<span class="token punctuation">)</span><span class="token punctuation">)</span>

r <span class="token operator">=</span> test<span class="token punctuation">(</span>a<span class="token punctuation">)</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;调用函数后 实参内存地址是 %x&quot;</span> <span class="token operator">%</span> <span class="token builtin">id</span><span class="token punctuation">(</span>a<span class="token punctuation">)</span><span class="token punctuation">)</span>
<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;调用函数后 返回值内存地址是 %x&quot;</span> <span class="token operator">%</span> <span class="token builtin">id</span><span class="token punctuation">(</span>r<span class="token punctuation">)</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br></div></div><h2 id="_02-可变和不可变类型"><a href="#_02-可变和不可变类型" class="header-anchor">#</a> 02. 可变和不可变类型</h2> <ul><li><p><strong>不可变类型</strong>，内存中的数据不允许被修改：</p> <ul><li>数字类型 <code>int</code>, <code>bool</code>, <code>float</code>, <code>complex</code>, <code>long(2.x)</code></li> <li>字符串 <code>str</code></li> <li>元组 <code>tuple</code></li></ul></li> <li><p><strong>可变类型</strong>，内存中的数据可以被修改：</p> <ul><li>列表 <code>list</code></li> <li>字典 <code>dict</code></li></ul></li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code>a <span class="token operator">=</span> <span class="token number">1</span>
a <span class="token operator">=</span> <span class="token string">&quot;hello&quot;</span>
a <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span>
a <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">1</span><span class="token punctuation">]</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br></div></div><div class="language-python line-numbers-mode"><pre class="language-python"><code>demo_list <span class="token operator">=</span> <span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">]</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;定义列表后的内存地址 %d&quot;</span> <span class="token operator">%</span> <span class="token builtin">id</span><span class="token punctuation">(</span>demo_list<span class="token punctuation">)</span><span class="token punctuation">)</span>

demo_list<span class="token punctuation">.</span>append<span class="token punctuation">(</span><span class="token number">999</span><span class="token punctuation">)</span>
demo_list<span class="token punctuation">.</span>pop<span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">)</span>
demo_list<span class="token punctuation">.</span>remove<span class="token punctuation">(</span><span class="token number">2</span><span class="token punctuation">)</span>
demo_list<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">10</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;修改数据后的内存地址 %d&quot;</span> <span class="token operator">%</span> <span class="token builtin">id</span><span class="token punctuation">(</span>demo_list<span class="token punctuation">)</span><span class="token punctuation">)</span>

demo_dict <span class="token operator">=</span> <span class="token punctuation">{</span><span class="token string">&quot;name&quot;</span><span class="token punctuation">:</span> <span class="token string">&quot;小明&quot;</span><span class="token punctuation">}</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;定义字典后的内存地址 %d&quot;</span> <span class="token operator">%</span> <span class="token builtin">id</span><span class="token punctuation">(</span>demo_dict<span class="token punctuation">)</span><span class="token punctuation">)</span>

demo_dict<span class="token punctuation">[</span><span class="token string">&quot;age&quot;</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">18</span>
demo_dict<span class="token punctuation">.</span>pop<span class="token punctuation">(</span><span class="token string">&quot;name&quot;</span><span class="token punctuation">)</span>
demo_dict<span class="token punctuation">[</span><span class="token string">&quot;name&quot;</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token string">&quot;老王&quot;</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;修改数据后的内存地址 %d&quot;</span> <span class="token operator">%</span> <span class="token builtin">id</span><span class="token punctuation">(</span>demo_dict<span class="token punctuation">)</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br></div></div><blockquote><p>注意：字典的 <code>key</code> <strong>只能使用不可变类型的数据</strong></p></blockquote> <p><strong>注意</strong></p> <ol><li><strong>可变类型</strong>的数据变化，是通过 <strong>方法</strong> 来实现的</li> <li>如果给一个可变类型的变量，赋值了一个新的数据，<strong>引用会修改</strong> <ul><li>变量 <strong>不再</strong> 对之前的数据引用</li> <li>变量 <strong>改为</strong> 对新赋值的数据引用</li></ul></li></ol> <h3 id="哈希-hash"><a href="#哈希-hash" class="header-anchor">#</a> 哈希 <code>(hash)</code></h3> <ul><li><code>Python</code> 中内置有一个名字叫做 <code>hash(o)</code> 的函数
<ul><li>接收一个 <strong>不可变类型</strong> 的数据作为 <strong>参数</strong></li> <li><strong>返回</strong> 结果是一个 <strong>整数</strong></li></ul></li> <li><code>哈希</code> 是一种 <strong>算法</strong>，其作用就是提取数据的 <strong>特征码（指纹）</strong> <ul><li><strong>相同的内容</strong> 得到 <strong>相同的结果</strong></li> <li><strong>不同的内容</strong> 得到 <strong>不同的结果</strong></li></ul></li> <li>在 <code>Python</code> 中，设置字典的 <strong>键值对</strong> 时，会首先对 <code>key</code> 进行 <code>hash</code> 已决定如何在内存中保存字典的数据，以方便 <strong>后续</strong> 对字典的操作：<strong>增、删、改、查</strong> <ul><li>键值对的 <code>key</code> 必须是不可变类型数据</li> <li>键值对的 <code>value</code> 可以是任意类型的数据</li></ul></li></ul> <h2 id="_03-局部变量和全局变量"><a href="#_03-局部变量和全局变量" class="header-anchor">#</a> 03. 局部变量和全局变量</h2> <ul><li><strong>局部变量</strong> 是在 <strong>函数内部</strong> 定义的变量，<strong>只能在函数内部使用</strong></li> <li><strong>全局变量</strong> 是在 <strong>函数外部定义</strong> 的变量（没有定义在某一个函数内），<strong>所有函数</strong> 内部 <strong>都可以使用这个变量</strong></li></ul> <blockquote><p>提示：在其他的开发语言中，大多 <strong>不推荐使用全局变量</strong> —— 可变范围太大，导致程序不好维护！</p></blockquote> <h3 id="_3-1-局部变量"><a href="#_3-1-局部变量" class="header-anchor">#</a> 3.1 局部变量</h3> <ul><li><strong>局部变量</strong> 是在 <strong>函数内部</strong> 定义的变量，<strong>只能在函数内部使用</strong></li> <li>函数执行结束后，<strong>函数内部的局部变量，会被系统回收</strong></li> <li>不同的函数，可以定义相同的名字的局部变量，但是 <strong>彼此之间</strong> 不会产生影响</li></ul> <h4 id="局部变量的作用"><a href="#局部变量的作用" class="header-anchor">#</a> 局部变量的作用</h4> <ul><li>在函数内部使用，<strong>临时</strong> 保存 <strong>函数内部需要使用的数据</strong></li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token keyword">def</span> <span class="token function">demo1</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    num <span class="token operator">=</span> <span class="token number">10</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span>

    num <span class="token operator">=</span> <span class="token number">20</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;修改后 %d&quot;</span> <span class="token operator">%</span> num<span class="token punctuation">)</span>


<span class="token keyword">def</span> <span class="token function">demo2</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    num <span class="token operator">=</span> <span class="token number">100</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span>

demo1<span class="token punctuation">(</span><span class="token punctuation">)</span>
demo2<span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;over&quot;</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br></div></div><h4 id="局部变量的生命周期"><a href="#局部变量的生命周期" class="header-anchor">#</a> 局部变量的生命周期</h4> <ul><li>所谓 <strong>生命周期</strong> 就是变量从 <strong>被创建</strong> 到 <strong>被系统回收</strong> 的过程</li> <li><strong>局部变量</strong> 在 <strong>函数执行时</strong> 才会被创建</li> <li><strong>函数执行结束后</strong> 局部变量 <strong>被系统回收</strong></li> <li><strong>局部变量在生命周期</strong> 内，可以用来存储 <strong>函数内部临时使用到的数据</strong></li></ul> <h3 id="_3-2-全局变量"><a href="#_3-2-全局变量" class="header-anchor">#</a> 3.2 全局变量</h3> <ul><li><strong>全局变量</strong> 是在 <strong>函数外部定义</strong> 的变量，所有函数内部都可以使用这个变量</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code><span class="token comment"># 定义一个全局变量</span>
num <span class="token operator">=</span> <span class="token number">10</span>


<span class="token keyword">def</span> <span class="token function">demo1</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span>


<span class="token keyword">def</span> <span class="token function">demo2</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span>

demo1<span class="token punctuation">(</span><span class="token punctuation">)</span>
demo2<span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;over&quot;</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br></div></div><p><strong>注意</strong>：函数执行时，<strong>需要处理变量时</strong> 会：</p> <ol><li><strong>首先</strong> 查找 <strong>函数内部</strong> 是否存在 <strong>指定名称 的局部变量</strong>，<strong>如果有，直接使用</strong></li> <li>如果没有，查找 <strong>函数外部</strong> 是否存在 <strong>指定名称 的全局变量</strong>，<strong>如果有，直接使用</strong></li> <li>如果还没有，程序报错！</li></ol> <h4 id="_1-函数不能直接修改-全局变量的引用"><a href="#_1-函数不能直接修改-全局变量的引用" class="header-anchor">#</a> 1) 函数不能直接修改 <code>全局变量的引用</code></h4> <ul><li><strong>全局变量</strong> 是在 <strong>函数外部定义</strong> 的变量（没有定义在某一个函数内），<strong>所有函数</strong> 内部 <strong>都可以使用这个变量</strong></li></ul> <blockquote><p>提示：在其他的开发语言中，大多 <strong>不推荐使用全局变量</strong> —— 可变范围太大，导致程序不好维护！</p></blockquote> <ul><li>在函数内部，可以 <strong>通过全局变量的引用获取对应的数据</strong></li> <li>但是，<strong>不允许直接修改全局变量的引用</strong> —— 使用赋值语句修改全局变量的值</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code>num <span class="token operator">=</span> <span class="token number">10</span>


<span class="token keyword">def</span> <span class="token function">demo1</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;demo1&quot;</span> <span class="token operator">+</span> <span class="token string">&quot;-&quot;</span> <span class="token operator">*</span> <span class="token number">50</span><span class="token punctuation">)</span>

    <span class="token comment"># 只是定义了一个局部变量，不会修改到全局变量，只是变量名相同而已</span>
    num <span class="token operator">=</span> <span class="token number">100</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span>


<span class="token keyword">def</span> <span class="token function">demo2</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;demo2&quot;</span> <span class="token operator">+</span> <span class="token string">&quot;-&quot;</span> <span class="token operator">*</span> <span class="token number">50</span><span class="token punctuation">)</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span>

demo1<span class="token punctuation">(</span><span class="token punctuation">)</span>
demo2<span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;over&quot;</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br></div></div><blockquote><p>注意：只是在函数内部定义了一个局部变量而已，只是变量名相同 —— 在函数内部不能直接修改全局变量的值</p></blockquote> <h4 id="_2-在函数内部修改全局变量的值"><a href="#_2-在函数内部修改全局变量的值" class="header-anchor">#</a> 2) 在函数内部修改全局变量的值</h4> <ul><li>如果在函数中需要修改全局变量，需要使用 <code>global</code> 进行声明</li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code>num <span class="token operator">=</span> <span class="token number">10</span>


<span class="token keyword">def</span> <span class="token function">demo1</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;demo1&quot;</span> <span class="token operator">+</span> <span class="token string">&quot;-&quot;</span> <span class="token operator">*</span> <span class="token number">50</span><span class="token punctuation">)</span>

    <span class="token comment"># global 关键字，告诉 Python 解释器 num 是一个全局变量</span>
    <span class="token keyword">global</span> num
    <span class="token comment"># 只是定义了一个局部变量，不会修改到全局变量，只是变量名相同而已</span>
    num <span class="token operator">=</span> <span class="token number">100</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span>


<span class="token keyword">def</span> <span class="token function">demo2</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>

    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;demo2&quot;</span> <span class="token operator">+</span> <span class="token string">&quot;-&quot;</span> <span class="token operator">*</span> <span class="token number">50</span><span class="token punctuation">)</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span>num<span class="token punctuation">)</span>

demo1<span class="token punctuation">(</span><span class="token punctuation">)</span>
demo2<span class="token punctuation">(</span><span class="token punctuation">)</span>

<span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;over&quot;</span><span class="token punctuation">)</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br><span class="line-number">17</span><br><span class="line-number">18</span><br><span class="line-number">19</span><br><span class="line-number">20</span><br><span class="line-number">21</span><br><span class="line-number">22</span><br><span class="line-number">23</span><br><span class="line-number">24</span><br></div></div><h4 id="_3-全局变量定义的位置"><a href="#_3-全局变量定义的位置" class="header-anchor">#</a> 3) 全局变量定义的位置</h4> <ul><li>为了保证所有的函数都能够正确使用到全局变量，应该 <strong>将全局变量定义在其他函数的上方</strong></li></ul> <div class="language-python line-numbers-mode"><pre class="language-python"><code>a <span class="token operator">=</span> <span class="token number">10</span>


<span class="token keyword">def</span> <span class="token function">demo</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">:</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;%d&quot;</span> <span class="token operator">%</span> a<span class="token punctuation">)</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;%d&quot;</span> <span class="token operator">%</span> b<span class="token punctuation">)</span>
    <span class="token keyword">print</span><span class="token punctuation">(</span><span class="token string">&quot;%d&quot;</span> <span class="token operator">%</span> c<span class="token punctuation">)</span>

b <span class="token operator">=</span> <span class="token number">20</span>
demo<span class="token punctuation">(</span><span class="token punctuation">)</span>
c <span class="token operator">=</span> <span class="token number">30</span>

</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br></div></div><p><strong>注意</strong></p> <ul><li>由于全局变量 c，是在调用函数之后，才定义的，在执行函数时，变量还没有定义，所以程序会报错！</li></ul> <p><strong>代码结构示意图如下</strong></p> <p><img src="media/14982751015713/001_%E4%BB%A3%E7%A0%81%E7%BB%93%E6%9E%84%E7%A4%BA%E6%84%8F%E5%9B%BE.png" alt="001_代码结构示意图-w240"></p> <h4 id="_4-全局变量命名的建议"><a href="#_4-全局变量命名的建议" class="header-anchor">#</a> 4) 全局变量命名的建议</h4> <ul><li>为了避免局部变量和全局变量出现混淆，在定义全局变量时，有些公司会有一些开发要求，例如：</li> <li>全局变量名前应该增加 <code>g_</code> 或者 <code>gl_</code> 的前缀</li></ul> <blockquote><p>提示：具体的要求格式，各公司要求可能会有些差异</p></blockquote></div></div> <!----> <div class="page-edit"><div class="edit-link"><a href="https://github.com/xugaoyi/vuepress-theme-vdoing/edit/master/docs/00.Python/16.变量进阶(理解).md" target="_blank" rel="noopener noreferrer">编辑</a> <span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></div> <!----> <!----></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/vdoing-demo-repository/pages/ed6fdd/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">15_名片管理系统(综合应用)</div></a> <a href="/vdoing-demo-repository/pages/f99095/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">17_函数进阶</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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